Sulfur dioxide scrubber with hydroclone separator

ABSTRACT

Sulfur dioxide is scrubbed from boiler flue gases in a double-loop alkali scrubber, one a quencher loop and the other an absorption loop. Preferably, the reagent flow of the two loops is isolated so that none of the reagent from the quencher loop is cycled to the absorber loop. A substantial portion of the make-up water for the quencher loop is received from the absorber loop and solids are concentrated in a dewatering system which includes a hydroclone.

This is a Division; of Application Ser. No. 957,674 filed Nov. 6, 1978now U.S. Pat. No. 4,250,152 granted Feb. 10, 1981.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to a unique doubleloop SO₂ scrubbing systemfor flue gas desulfurization which achieves substantially complete limeor limestone utilization concurrently with high SO₂ scrubbingefficiency, and excellent corrosion control.

2. Description of the Prior Art

Scrubbing of boiler flue gases with slurries of limestone (CaCO₃) orcalcined limestone products, lime and hydrated lime, is a known andsimple method for the removal of sulfur dioxide (SO₂) from thesecombustion gases. The system does, however, require makeup water foroperation and therefore increases the total plant demand for water. Assuitable quality water is often available to the plant only in limitedquantities, it is essential that the scrubbing system use a minimum ofhigh quality makeup water.

Makeup water is required in sulfur dioxide scrubbing systems to replacewater lost in two areas: (1) water lost through evaporation as a meansof saturating the incoming gases; and (2) water lost with the solidwaste product composed of unreacted reagent, calcium sulfite hydratesand calcium sulfate hydrites that are discharged from the system. Thetotal makeup water requirements for the system can, therefore, beminimized by reducing these water losses.

Generally makeup water enters the sulfur dioxide scrubbing system inseveral areas: (1) water entering with the reagent; (2) water for slurrypump packing glands; (3) wash water to remove solids that have built upon impingement-type demisters; (4) quencher makeup water, which replacesmost of the evaporative losses. Most of the makeup water is eitherdemister wash water or quencher makeup water. The water used as demisterwash water must be of sufficiently high quality so as not to contributeto the solids build-up it is designated to wash away. Its solids contentand pH must be kept within limits. The quencher makeup water, on theother hand, can be of considerably lesser quality.

One prior art method for minimizing system water losses (i.e. processmakeup water requirements) is to operate the scrubbing system in aclosed loop manner. In closed loop operation, the discharge slurry fromthe scrubbing system is partially dewatered to generate two new streams;a high solids stream that is sent to disposal; and a low quality waterstream that is recycled to the scrubbing system.

Utilization of this recycled water can reduce the overall process freshmakeup water requirements by up to 50%. However, the recycled water issaturated in sulfates which increases the potential for scaling in theflue gas desulfurization system. In addition, impurities includingcorrosive chlorides are concentrated within the SO₂ Removal Systemduring closed loop operation. These impurities force the use of exoticand expensive materials of construction and often preclude closed loopoperation in single loop desulfurization systems.

SUMMARY OF THE INVENTION

It is known that a solution to these problems is to operate the processin two loops, and to isolate the demisters, which cannot accept recycledwater, from the evaporative portion of the process which requiresquencher makeup water; then to send all of the recycled water back tothe evaporative "quencher" loop and none to the loop containing thedemisters and the primary absorber sections. The present invention addsto such system a unique system for selectively separating certain of thesolids and the liquid from the quencher recycle water.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described in reference to thedrawings wherein:

FIG. 1 is a simplified flow diagram of the system;

FIG. 2 is a partial sectional diagrammatic view of a multi-stagequencher-absorber tower useful for carrying out the system of theinvention;

FIG. 3 is an enlarged partial sectional view of a hydroclone useful inthe system of the invention; and

FIG. 4 is a section on line 4--4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, 10 generally designates a system ofthe invention and the system includes a multiple-stage quencher-absorbertower 12, to be more fully described in reference to FIG. 2, whichincludes a quencher 14 and an absorber 16.

Arrows 18a, b and c designate respectively the gas flow to the quencher14, gas flow from the quencher 14 to the absorber and the SO2 strippedflue gas.

Other primary components of the system include absorber tank 20,quencher tank 22, dewatering system 24 comprising a hydroclone 24aillustrated in FIGS. 3 and 4, an absorber separator 26, pumps 28, 30 and32, each of which has a pump seal water inlet designated 34a, b and cfor pumps 32, 30 and 28 respectively.

The primary liquids/slurry lines for the system are: line 36 from theabsorber tank 20 to pump 28; line 38 comprising the primary absorberfeed line from the pump 28 to the absorber 16; secondary absorber feedline 40 from absorber tank 20 to pump 38; secondary absorber feed line42 from pump 30 to absorber 16; line 44 comprising a branch of line 42from the secondary absorber feed to the absorber separator 26; line 46from the absorber 16 to the absorber tank 20, the demister wash waterline 48 for the multi-stage quencher-absorber tower 12; line 50 thereagent feed line for absorber tank 20; overflow line 52 from theabsorber separator 26 to absorber tank 20; underflow line 54 from theabsorber separator 26; absorber tank 20 overflow line; the quencher tankfeed line 56; line 58 from quencher tank 22 to pump 32; line 60comprising the quencher feed line from pump 32 to the quencher 14;quencher return line 62 from quencher 14 to quencher tank 22; line 64comprising the discharge from the quencher tank 22 to the dewateringsystem 24; line 66 from the dewatering system 24 to the quencher tank22; and line 68 comprising the dewatering system blow down line fromdewaterer 24.

Referring now to FIG. 2, the multi-stage quencher-absorber tower 12 hasa vertically extending shell 70 with a flue gas inlet 72 adjacent to thelower end and a SO₂ stripped flue gas outlet 73 at the upper end. Belowthe flue gas inlet 72 is a sump 74 provided with a sump stirringmechanism generally designated 76. From the sump is connected line 62,the return line from the quencher to the quencher tank 22.

In FIG. 2, the quencher section is generally designated 14 and theabsorber section is generally designated 16. The quencher sectionincludes a plurality of headers 80, which would be connected to line 60from the pump 32, with each of the headers being provided with aplurality of spray outlet nozzles 82. In a preferred embodiment, thequencher section 14 is of the cyclonic type as the flue gases enteringinlet 72 are caused to flow tangentially upwardly.

Between the quencher section 14 and the absorber section 16 is agas/liquid bowl separator generally designated 84. This separator 84collects the water from the demister and the treating fluid from theabsorber and the collected fluid is directed from the separator 84, forreturn to the absorber tank, via line 46. Above the bowl separator 84are a plurality of headers designated 86 and 86a each having connectionto lines 42 and 38 comprising the primary and secondary absorber feedlines.

Each of the headers 86 and 86a is provided with a plurality of spraytype outlet nozzles 88 and between the headers 86 and 86a is aconventional packed tower arrangement 90. Above the upper most header86a is arranged lower demister 92 and upper demister 94. Wash water forthe lower demister is provided via header 96 having spray type outlets98. The upper demister 94 is also provided with a wash liquid meansincluding a header 100 provided with spray type outlets 102.

Referring now to FIGS. 3 and 4, the hydroclone 24a is provided with atangential inlet 104, which is fed the slurry to be dewatered via line64. The fluid entering the hydroclone 24a via the tangential inlet 104swirls about a vortex finder 106. The swirling slurry concentrates flowdown the cone section 108 to the apex opening 110 thence out theunderflow via line 68. The partially clarified slurry passes upwardlythrough the vortex finder 106 to the outlet 112 then to conduit 66 forreturn to the quencher tank 22. Lines 64 and 68 are provided withhydroclone control valves 104' and 106'.

The centrifugal separation forces of the hydroclone were found to veryeffectively selectively concentrate calcium sulfate in the underflowwhile the overflow recycles the remaining slurry constituents back intothe main quencher feed systems. The effectiveness of the hydrocloneassures virtually complete lime utilization in the flue gasdesulfurization process all as to be more fully described hereinafter.

Referring again to the drawings of the present invention, the two-loopprocess includes a quencher loop A wherein almost all of the evaporativewater losses occur, and an absorber loop B (which includes the demisters92-94), wherein gases pass first through the quencher loop, then throughthe absorber loop. Reagent flow is counter-current to the gas flow,passing first through the absorber loop. Solids are removed from thesystem as follows: Solids products of the reaction between the calciumbased reagent and sulfur dioxide, as well as some unreacted reagent, arefed from the absorber loop B to the quencher along A with some water.The solids are then circulated through the quencher loop A wherein morereaction products are formed as the concentration of unreacted reagentdecreases. The solids are then discharged from the quencher to thedewatering system 24 and ultimate waste disposal.

Makeup water enters the absorber loop as: (1) water entering with thereagent at 50; (2) water for slurry pump packing glands at 34a and b;and (3) demister wash water at 48. Makeup water enters the quencher loopas: (1) fresh makeup water for slurry pump packing glands at 34a; (2)quencher makeup water (recycled water) at 66, which replaces most of theevaporative losses; and (3) water accompanying the absorber loopdischarge solids at 54.

If and when the process requirement for quencher makeup water is equalto the recycled water generated by the sludge dewatering systems,optimum water utilization is achieved. However, the process requirementfor quencher makeup water is directly related to the volume of flue gastreated. The recycled water is generated (for a given mode of disposalsolids dewatering) is directly related to both the volume of gas treatedand the concentration of sulfur dioxide in the gas. Therefore, there isonly one precise sulfur dioxide concentration for any given treated gasvolume for which the process requirement for quencher makeup waterequals the recycled water available for return to the process. As aresult, there are many operating conditions when the recycled water thatis available exceeds or is less than the quencher makeup waterrequirement.

For those operating conditions where the recycled water generatedexceeds the quencher makeup water requirement, the water accompanyingthe absorber loop discharge solids must be reduced in order to permitall of the recycled water to enter the quencher loop. By doing this, norecycled water is sent to the absorber loop and in particular to thedemister wash sprays, while maintaining closed loop operation.

For those operating conditions where the recycled water generated isless than the quencher makeup water requirement, it is desirable toincrease the water accompanying the absorber loop discharge solids. Thewater used to increase this flow is added to the process as demisterwash water, thereby achieving the goal of maximizing demister wash waterrelative to the total fresh makeup water requirement.

In both cases, it is desired to vary the amount of water exiting withthe absorber loop discharge solids without affecting the operation ofthe absorber circuit. This is done through the use of solid/liquidseparating hydroclone 24a. The hydroclone treats a portion of theabsorber loop slurry to generate two streams, a high solids stream and alow solids stream. Either of these streams can be combined with anappropriate quantity of untreated absorber loop slurry to produce astream containing solids equal to the rate of solids build-up in theabsorber circuit along with any quantity of water attainable from themixing of these two streams. With the approach, a wide range of solidscontents is attainable in the absorber discharge stream.

For those operating conditions where the recycled water generatedexceeds the quencher makeup water requirement, the high solids stream iscombined with untreated absorber discharge slurry to reduce the totalamount of water accompanying the absorber discharge solids. For thoseoperating conditions where the recycled water generated is less than thequencher makeup water requirement, the low solids stream is combinedwith untreated absorber discharge slurry to increase the total amount ofwater accompanying the absorber discharge solids.

Because plant operating conditions (i.e. load factor and fuel sulfurcontent) are constantly varying, the rate of solids generation in theabsorber circuit, and the amount of water required to enter the quenchercircuit with those solids, are also constantly changing. To allow thesolid/liquid separator system to react to the instantaneous processrequirements for water versus solids in the absorber discharge slurry, asulfur dioxide mass flow signal 110 is used. This signal is fed to acontroller (not shown) which relates the volume of gas treated and theconcentration of sulfur dioxide in the gas to the rate of recycled watergeneration as well as to the rate of absorber discharge solidsgeneration and determines the ratio of treated absorber discharge slurryto untreated absorber discharge slurry. The controller also determineswhether the high solids stream or the low solids stream should be mixedwith the untreated absorber discharge slurry. Therefore, with thiscontrol scheme, the quencher circuit can receive the amount of waterfrom the absorber circuit that it requires under all process operationconditions.

The primary advantage of using a hydroclone 24a is that the hydrocloneaccomplishes a chemical separation rather than a separation basedstrictly on particle size. The constituents in the feed stream via line64 to the hydroclone 24a would normally include:

CaSO₄.2H₂ O Gypsum

CaSO₃.1/2 H₂ O

CaCO₃

Ca (OH)₂ in some cases

Gangue from the lime or limestone

Fly Ash Fines

Chips from scale deposits in the scrubber

Test data indicate that by making appropriate adjustments in thehydroclone operating parameters, namely, the feed rates and under flowrates via valves 104' and 106' the chemical compositions of theunderflow and overflow can be controlled. While it is true that theseparation is determined by particle size and density differences, theessence of the invention is the ability to control the chemicalcomposition of the underflow and overflow streams.

This ability to control the system's chemical constituents has severalvery important results. First, the separation can be controlled, whenCa(OH)₂ or finely ground limestone (CaCO₃) is used as the scrubbingreagent, to essentially eliminate the presence of Ca(OH)₂ or CaCO₃ inthe hydroclone underflow, the system effluent. This will substantiallyincrease the utilization factor for these reagents in the scrubbingprocess. The cost of these reagents makes up 10 to 30% of the normaloperating expense of the systems and this invention can reduce theirconsumption by up to 20% thereby reducing the overall operating cost byas much as 6%. For a typical utility system this saving is approximately$1,000,000 per year.

Second, by utilizing a hydroclone in the system, via the ability tocontrol the chemical compositions of the various streams, the hydroclonewill maximize the gypsum content of the hydroclone underflow when an insitu oxidation system is being utilized or where naturally high sulfiteoxidation occurs. This approach produces a waste product stream thatpossesses very desirable dewatering, blending and disposal properties.This can substantially reduce the investment and operating costsincurred for final sludge dewatering and disposal. In addition, itprovides a means of recycling smaller gypsum crystals as well asunoxidized CaSO₃.1/2H₂ O to the system for further oxidation and crystalgrowth. This ability to remove the desirable gypsum selectively allowsfor a simpler oxidizer design since complete oxidation and maximumcrystal size need not be obtained directly in the oxidation system.

The operation of the hydroclone in the system of the present inventionwill be more fully understood from the following examples. In theexamples, the only control variables were the inlet pressure to thehydroclone (flow rate) and the ratio of overflow to underflow. Theseconditions were varied by throttling the two valves 104' and 106'located at the inlet and outlet of the hydroclone. A filter was placedon the bottom cone 68 of the hydroclone in four of the tests (runs 7through 10, Table I) in an effort to produce higher % solids in theunderflow.

A total of eleven runs were conducted. Flow rates for the overflow andunderflow were measured during each run by using a calibrated bucket andstopwatch. The pressure drop across the hydroclone was taken and fieldanalyses were run on overflow and underflow samples for pH and % solids.Other samples were filtered for analysis and determination of particlesize distribution. The highest solids concentration attained in theunderflow under reproducible conditions was 61.0% dry solids (87.6%solids was obtained in run #1, but could not be verified in a laterduplicate test). Overflow concentrations appeared to be independent ofprocess conditions, remaining close to an average value of 4.05% solids.

Filtered overflow and underflow samples from each run were submitted tothe laboratory for thermogravimetric analysis (TGA) to determine thesulfate and sulfite concentrations, and for analysis to determine thepercentage of acid insolubles and loss on ignition. A summary of thedata is presented in Table II. The composition of the underflow sludgeis of most interest and the sulfate (CaSO₄.2H₂ O) concentration in theunderflow was surprisingly high, varying slightly more than 5% around amean of 95.93%. Acid insolubles averaged 3.8% in the underflow samples,indicating little or no sulfite or unreacted lime present. A check ontotal alkalinity of the high pH test samples confirmed this.

The overflow samples contained a substantial amount of fine unburnedcarbon, as indicated by the relatively high (25.96%) average loss onignition. The overflow composition averaged out to 39.8% sulfate and58.87% acid insolubles.

Particle size distribution of unfiltered samples was determined by wetsieve analysis. Almost 100% of the overflow particulate was finer than44μ, the smallest test sieve available. The underflow had a somewhatbroader distribution, with up to 19% of the particulate in the 44 to 74μrange, although more than 80% was finer than 44μ in all cases.

The abundance of sulfate in the underflow is explainable based on thetheory of operation of the hydroclone. The hydroclone uses centrifugalforce to separate the smaller low density particles from the larger highdensity particles in the incoming sludge. Calcium sulfate is the largestparticle present and separates more easily forming the majority of theunderflow, while smaller particles form the bulk of the overflow.

The magnitude of the sulfate concentration in the underflow wasunexpected. An average of almost 96% CaSO₄.2H₂ O for all runs regardlessof feed concentration (normal maximum 70% sulfate) was observed. It wasfound that the sulfate concentration varies directly with the solidsconcentration of the underflow, with a maximum of 98% attainable, butwith relatively little change above 55% solids.

The noted absence of unreacted lime in the underflow implies that thelime is being recycled back into the system with the hydrocloneoverflow. Laboratory analysis for total alkalinity in the underflowsludge from runs #9 and #11 confirmed the low lime content (0 to 1.29%)even at high slurry pH. This indicates that high lime utilization can beachieved at virtually any sulfur dioxide removal efficiency desired dueto the efficient separation of the unreacted lime in the hydroclone.Also, the sludge thickening capability of the hydroclone appears to beindependent of slurry pH.

The sulfate concentration and % solids in the hydroclone underflowsludge is a function of the ratio of the flow rates(overflow/underflow). The amount of overflow obtained was proportionalto the pressure drop across the hydroclone.

                                      TABLE I                                     __________________________________________________________________________    HYDROCLONE PERFORMANCE TEST RESULTS                                                                     Pressure Drop                                       Run                                                                              Flow Rate, GPM                                                                            Ratio      Across Hydro-                                                                         % Solids                                    No.                                                                              Overflow                                                                            Underflow                                                                           Overflow/Underflow                                                                       Clone, psi                                                                            Overflow                                                                            Underflow                                                                           pH                              __________________________________________________________________________    1  15.36 3.35  4.58       24.0    4.9   (87.6).sup.a                                                                        --                              2  15.04 3.61  4.17       23.0    4.0   61.0  --                              3  9.45  4.36  2.16       18.1    4.7   41.3  5.1                             4  6.25  8.01  0.78       13.3    4.0   26.7  3.1                             5  0.78  13.91 0.056      7.5     3.7   19.6  3.3                             6  13.65 5.71  2.39       22.8    3.9   42.7  4.4                             7  9.57  2.89  3.31       .2      3.9   47.1  3.4                             8  0.0.sup.b                                                                           4.23  0.0        40.2    --    24.3  7.8                             9  12.71 5.38  2.36       20.2    3.8   41.7  8.2                             10 14.45 2.39  6.05       22.8    3.7   59.2                                  11 11.52 5.46  2.11       23.2    3.9   31.6  7.1                             __________________________________________________________________________     .sup.a Result appears to be in error.                                         .sup.b The pressure head in this test was not high enough to pump any         overflow up to the top of the dissolver tank (approx. 20 feet).          

                  TABLE II                                                        ______________________________________                                        TGA RESULTS                                                                                                        % Loss                                                                        On Ig-                                                                        nition                                   Run  % CaSO.sub.4.2H.sub.2 O                                                                       % Acid Insolubles                                                                             Over-                                    No.  Overflow  Underflow Overflow                                                                              Underflow                                                                             flow                                 ______________________________________                                        1    41.57     97.77     58.15   1.50    26.5                                 2    39.18     97.72     61.49   4.47    28.0                                 3    47.78     97.34     58.49   3.44    26.5                                 4    43.96     96.28     53.05   3.02    25.6                                 5    22.94     90.79     76.22   9.83    34.2                                 6    32.49     96.52     66.33   1.89    22.8                                 7    38.23     96.52     60.35   1.58    22.3                                 8    --        92.08     --      8.08    --                                   9    43.01     94.37     52.16   2.83    24.1                                 10   46.83     97.31     49.15   1.85    22.7                                 11   42.05     98.58     53.30   3.28    26.9                                 Av-                                                                           er                                                                            age  39.80     95.93     58.87   3.80    25.96                                ______________________________________                                    

The following examples, designated Case 1 and Case 2 for a high sulfurcontaining gas stream and a medium sulfur containing gas stream willfurther delineate the present invention.

    ______________________________________                                        ASSUMPTIONS                                                                   Cases 1 and 2                                                                 ______________________________________                                        (1)   Absorber Tower Efficiency =                                                                       90%                                                       Quencher Efficiency =                                                                             30%                                                       Absorber Efficiency =                                                                             85.71%                                              (2)   Reagent Utilization =                                                                             95%                                                 (3)   Limestone Purity =  95%                                                 (4)   No fly ash absorbed into slurry streams                                 (5)   Forced oxidation in quencher to 95% mole fraction                             CaSO.sub.4.2H.sub.2 O                                                   (6)   80% solids blowdown to ultimate disposal (fully                               closed loop)                                                            ______________________________________                                    

    ______________________________________                                        CASE 1                                                                        High Sulfur (3,000 ppmw) case                                                 Absorber feed to quencher = 25.33% solids                                     CASE 5                                                                        Medium Sulfur (1,500 ppmw) case                                               Absorber feed to quencher = 15.34% solids                                     ______________________________________                                    

    ______________________________________                                        STREAMS                                                                       CASES 1 and 2                                                                 ______________________________________                                        18a  GAS IN                                                                   18b  GAS                                                                      18c  GAS OUT                                                                  50   REAGENT FEED                                                             34c  PRIMARY ABSORBER PUMP SEAL WATER                                         34b  SECONDARY ABSORBER PUMP SEAL WATER                                       48   DEMISTER WASH WATER                                                      38   PRIMARY ABSORBER FEED                                                    42   SECONDARY ABSORBER FEED                                                  44   ABSORBER SEPARATOR FEED                                                  52   ABSORBER SEPARATOR OVERFLOW                                              54   ABSORBER SEPARATOR UNDERFLOW                                             56   ABSORBER TANK OVERFLOW                                                   56'  SLURRY FEED TO QUENCHER FROM ABSORBER                                    34a  QUENCHER PUMP SEAL WATER                                                 66   DISPOSAL RETURN WATER                                                    60   QUENCHER FEED                                                            64   DISCHARGE TO DEWATERING SYSTEM                                           68   DEWATERING SYSTEM BLOWDOWN                                               EL   EVAPORATIVE LOSSES                                                       ______________________________________                                    

    __________________________________________________________________________    GAS STREAMS                                                                   CASE 1                                                                        GAS IN - 18a                                                                      lb/hr lb moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,207,421                                                                           43,122                                                                              767,000                                                                             DENSITY                                                                              °                                                                        0.0550 lb/ft.sup.3                             CO.sub.2                                                                          296,852                                                                             6,747 120,000                                                                             TEMP   °                                                                        280° F.                                 O.sub.2                                                                            53,973                                                                             1,687  30,000                                                                             PRESSURE                                                                             °                                                                        8.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                           10,795                                                                               169  3,000                                                                              MW     °                                                                        29.348 LB/                                     H.sub.2 O                                                                          80,959                                                                             4,497  80,000        LB MOLE                                        Total                                                                             1,650,000                                                                           56,222                                                                              1,000,000                                                                           ACFM   °                                                                        500,00                                         __________________________________________________________________________    GAS SATURATED - 18b                                                               lb/hr lb/moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,207,421                                                                           43,122                                                                              730,447                                                                             DENSITY                                                                              °                                                                        0.0707 lb/ft.sup.3                             CO.sub.2                                                                          299,079                                                                             6,797 115,135                                                                             TEMP   °                                                                        125° F.                                 O.sub.2                                                                            49,484                                                                             1,456  26,188                                                                             PRESSURE                                                                             °                                                                        5.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                             7,556.5                                                                            118.07                                                                             2,000                                                                              MW     °                                                                        28.757 LB/                                     H.sub. 2 O                                                                        134,144                                                                             7,452 126,230        LB MOLE                                        Total                                                                             1,697,685                                                                           59,035                                                                              1,000,000                                                                           ACFM   °                                                                        400,000                                        __________________________________________________________________________    GAS OUT - 18c                                                                     lb/hr lb moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,207,421                                                                           43,122                                                                              732,423                                                                             DENSITY                                                                              °                                                                        0.0701 lb/ft.sup.3                             CO.sub.2                                                                          303,532                                                                             6,898 117,161                                                                             TEMP   °                                                                        125° F.                                 O.sub.2                                                                            44,379                                                                             1,387  23,558                                                                             PRESSURE                                                                             °                                                                        3.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                             1,709.5                                                                             16.87                                                                               287                                                                              MW     °                                                                        28.71 LB/                                      H.sub.2 O                                                                         134,144                                                                             7,452 126,571        LB MOLE                                        Total                                                                             1,690,556                                                                           58,876                                                                              1,000,000                                                                           ACFM   °                                                                        401,951                                        __________________________________________________________________________

    __________________________________________________________________________    LIQUID STREAMS                                                                CASE 1                                                                        Stream                                                                             lb/hr                                                                             lb/hr  lb/hr  lb/hr                                                                             lb/hr                                                                              lb/hr                                                                              GPM %   ppm                              Number                                                                             CaCO.sub.3                                                                        CaSO.sub.3.1/2H.sub.2 O                                                              CaSO.sub.4.2H.sub.2 O                                                                Inerts                                                                            Water                                                                              Total                                                                              Total                                                                             Solids                                                                            CHlorides                        __________________________________________________________________________    50   15,980                                                                            0      0      841 31,239                                                                             48,060                                                                             76  35  1,000                            34c  0   0      0      0   5,000                                                                              5,000                                                                              10  0   1,000                            34b  0   0      0      0   2,500                                                                              2,500                                                                              5   0   1,000                            48   0   0      0      0   22,812                                                                             22,812                                                                             45  0   1,000                            38   273,759                                                                           505,427                                                                              135,525                                                                              39,289                                                                            3,586,000                                                                          9,540,000                                                                          18,000                                                                            10  1,023                            42   114,066                                                                           210,595                                                                              56,469 16,370                                                                            3,577,500                                                                          3,975,000                                                                          7,500                                                                             10  1,023                            44   8,276                                                                             15,279 4,097  1,188                                                                             259,560                                                                            288,100                                                                            544 10  1,023                            52   3,547                                                                             6,548  1,756  509 234,840                                                                            247,200                                                                            480 5   1,023                            54   4,729                                                                             8,731  2,341  679 24,720                                                                             41,200                                                                             64  40  1,023                            56   1,131                                                                             2,088  560    162 35,469                                                                             39,410                                                                             72  10  1,023                            56'  5,860                                                                             10,819 2,901  841 60,189                                                                             80,610                                                                             136 25.33                                                                             1,023                            34a  0   0      0      0   3,750                                                                              3,750                                                                              7.5 0   9,525                            66   0   0      0      0   148,547                                                                            148,547                                                                            297 0   9,525                            60   23,818                                                                            29,184 739,429                                                                              25,069                                                                            4,632,500                                                                          5,450,000                                                                          10,000                                                                            15  9,525                            64   799 979    24,805 841 155,403                                                                            182,827                                                                            335 15  9,525                            68   799 979    24,805 841 6,856                                                                              34,280                                                                             38  80  9,525                            EL   0   0      0      0   53,185                                                                             53,185                                                                             106 0      0                             __________________________________________________________________________

    __________________________________________________________________________    GAS STREAMS                                                                   CASE 2                                                                        GAS IN - 18a                                                                      lb/hr lb moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,202,656                                                                           42,952                                                                              767,000                                                                             DENSITY                                                                              °                                                                        .0547 lb/ft.sup.3                              CO.sup.2                                                                          295,680                                                                             6,720 120,000                                                                             TEMP   °                                                                        280° F.                                 O.sub.2                                                                            53,760                                                                             1,680  30,000                                                                             PRESSURE                                                                             °                                                                        8.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                           5,376                                                                                84   1,500                                                                              MW     °                                                                        29.279 lb                                      H.sub.2 O                                                                          82,152                                                                             4,564  81,500        lb/mole                                        Total                                                                             1,639,624                                                                           56,000                                                                              1,000,000                                                                           ACFM   °                                                                        500,000                                        __________________________________________________________________________    GAS SATURATED - 18b                                                               lb/hr lb moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,202,656                                                                           42,952                                                                              728,460                                                                             DENSITY                                                                              °                                                                        .0705 lb/ft.sup.3                              CO.sub.2                                                                          296,789                                                                             6,745 114,394                                                                             TEMP   °                                                                        125° F.                                 O.sub.2                                                                            52,655                                                                             1,645  27,899                                                                             PRESSURE                                                                             °                                                                        5.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                             3,763.2                                                                            58.8                                                                                 997                                                                              MW     °                                                                        28.696 lb                                      H.sub.2 O                                                                         136,120                                                                             7,562 128,250        lb/mole                                        Total                                                                             1,691,983                                                                           58,963                                                                              1,000,000                                                                           ACFM   °                                                                        400,000                                        __________________________________________________________________________    GAS OUT - 18c                                                                     lb/hr lb moles/hr                                                                         ppm                                                           __________________________________________________________________________    N.sub.2                                                                           1,202,656                                                                           42,952                                                                              728,499                                                                             DENSITY                                                                              °                                                                        .0701                                          CO.sub.2                                                                          299,007                                                                             6,796 115,267                                                                             TEMP   °                                                                        125° F.                                 O.sub.2                                                                            52,521                                                                             1,641  27,833                                                                             PRESSURE                                                                             °                                                                        3.0 IWC @ SEA                                                                 LEVEL                                          SO.sub.2                                                                             537.6                                                                               8.4                                                                                 142                                                                              MW     °                                                                        28.618 lb                                      H.sub.2 O                                                                         136,120                                                                             7,562 128,259        lb/mole                                        Total                                                                             1,690,842                                                                           58,959                                                                              1,000,000                                                                           ACFM   °                                                                        401,951                                        __________________________________________________________________________

    __________________________________________________________________________    LIQUID STREAMS                                                                CASE 2                                                                        Stream                                                                             lb/hr                                                                             lb/hr  lb/hr  lb/hr                                                                             lb/hr                                                                              lb/hr                                                                              GPM %   ppm                              Number                                                                             CaCO.sub.3                                                                        CaSO.sub.3.1/2H.sub.2 O                                                              CaSO.sub.4.2H.sub.2 O                                                                Inerts                                                                            Water                                                                              Total                                                                              Total                                                                             Solids                                                                            Chlorides                        __________________________________________________________________________    50   7,958                                                                             0      0      419 15,557                                                                             23,934                                                                             38  35  1,000                            34c  0   0      0      0   5,000                                                                              5,000                                                                              10  0   1,000                            34b  0   0      0      0   2,500                                                                              2,500                                                                              5   0   1,000                            48   0   0      0      0   33,767                                                                             33,767                                                                             67  0   1,000                            38   243,310                                                                           449,265                                                                              120,488                                                                              34,937                                                                            7,632,000                                                                          8,480,000                                                                          16,000                                                                            10  1,012                            42   60,828                                                                            112,316                                                                              30,122 8,734                                                                             1,908,000                                                                          2,120,000                                                                          4,000                                                                             10  1,012                            44   2,370                                                                             4,376  1,174  340 74,340                                                                             82,600                                                                             156 10  1,012                            52   1,016                                                                             1,876  503    140 67,263                                                                             70,805                                                                             138 5   1,012                            54   1,354                                                                             2,500  671    194 7,077                                                                              11,795                                                                             18  40  1,012                            56   1,564                                                                             2,888  774    235 49,069                                                                             54,521                                                                             103 10  1,012                            56'  2,918                                                                             5,388  1,445  419 56,146                                                                             66,316                                                                             121 15.34                                                                             1,012                            34a  0   0      0      0   2,500                                                                              2,500                                                                              5   0   1,000                            66   0   0      0      0   73,980                                                                             73,980                                                                             148 0   16,640                           60   19,058                                                                            23,367 591,512                                                                              20,063                                                                            3,706,000                                                                          4,360,000                                                                          8,000                                                                             15  16,640                           64   398 488    12,353 419 77,395                                                                             91,053                                                                             167 15  16,640                           68   398 488    12,353 419 3,415                                                                              17,073                                                                             19  80  16,640                           EL   0   0      0      0   53,958                                                                             53,968                                                                             108 0      0                             __________________________________________________________________________

    __________________________________________________________________________    Ranges of Stream Solids Contents                                              __________________________________________________________________________    Stream Number                                                                             52      54       56      56'                                      Stream Name ABSORBER                                                                              ABSORBER ABSORBER                                                                              SLURRY FEED TO                                       SEPARATOR                                                                             SEPARATOR                                                                              TANK    QUENCHER FROM                                        OVERFLOW                                                                              UNDERFLOW                                                                              OVERFLOW                                                                              ABSORBER                                 Range of % Solids                                                                         3-10    10-50    5-15    3-50                                     Hi Sulfur % Solids                                                                        5       40       10      25.33                                    (Case 1)                                                                      Medium Sulfur % Solids                                                                    5       40       10      15.34                                    (Case 2)                                                                      __________________________________________________________________________

We claim:
 1. Apparatus for removing sulfur dioxide from flue gas comprising:a quencher-absorber tower; a flue gas quencher; and a flue gas scrubber serially mounted in said tower; a flue gas inlet for said tower in communication with said flue gas quencher; gas outlet means for said tower in communication with the flue gas scrubber; means for serially passing the flue gas first through the quencher and then through the scrubber; an alkali reagent water slurry; means for serially contacting the gas first in the quencher and then in the scrubber with the alkali/water slurry; dewatering means for a portion of the partially spent alkali reagent water slurry; said dewatering means comprising a hydroclone, a tangential inlet at the upper end of the hydroclone, a bottom outlet for discharging heavy particles from the hydroclone, a vortex finder mounted in the upper end of the hydroclone forming the light fraction discharge from the hydroclone, a slurry feed control valve for the tangential inlet, a heavy particle control valve for the bottom outlet and means for directing the lighter fraction discharged from the hydroclone into the alkali/water slurry for the gas quencher. 